There are known in the prior art sunglasses and safety eyewear intended to protect the wearer's eye against the harmful effects of sunlight, as well against flying objects and the like which might otherwise strike the wearer's eye. In general, two forms of eyewear of this type are available in the prior art. The first is a spectacle in which individual lenses are mounted in a frame. A second type is one in which a spectacle with two lenses is fabricated in one piece with an integral bridge but with separate optical axes for the lens. In both of these types, the lenses themselves are of overall spherical or toric construction.
Modern design of sunglasses and safety eyewear calls for lenses with large diameters and steeply "wrapped" configurations. With lenses of such large diameter and steep wraps, the result is a lens of non-uniform thickness which may add to the weight of the lens and result in different transmission properties across the lens in the case of absorptive lenses such as sunglasses.
Another approach is to use a face form angle wherein the optical axis is angled and the optical center is near the center of the angled lens. In this way, the true optical size is limited and a more uniform thickness is provided. While it affords a lighter weight lens with the same appearance as one having correct optical axes parallel to the line of sight, it creates prism imbalance for all angles of view.
A third class of eye protectors is the one-piece face shield type having but one optical axis passing through the optical center halfway between the eyes. The eye protector is of an overall spherical or toric surface shape. Owing to the large overall diameter of this one-piece design, maintaining uniform thickness can be an even greater problem than with two lens type glasses. This is particularly true if the lens has sufficient diameter and depth to provide protection for both eyes through an outward field of view of approximately 90 degrees or greater. To achieve such a wide field of view, a break in the curve may be employed resulting in a parting line in a molded product where the outer wrap area is of a different curve and usually not of true optical quality. Alternatively, side shields might be used. Such an arrangement, however, provides an even greater interruption of vision in the outer peripheral area of the lens.